Synchronous electric machine

ABSTRACT

A synchronous electric machine having a stator is provided with a polyphase winding producing a rotating magnetic filed and an annular D.C. winding to produce a coaxial steady field. Sets of rotor poles are disposed in axially spaced transverse planes and permanent magnets consisting of ceramic material of high coercivity and having radially inner and outer faces of opposite polarity are disposed in each transverse plane between the poles, the polarity of the radially outer faces of the permanent magnets being opposed to that induced in adjacent poles by the D.C. winding.

[75] Inventor:

United States Patent 1 de Jong SYNCHRONOUS ELECTRIC MACHINE HenricusCornelis Johannes de Jong, Hengelo, Netherlands [73] Assignee: HeemafN.V., l-lengelo, Netherlands [22] Filed: Dec. 20, 1971 [21] Appl. No.:209,614

[30] Foreign Application Priority Data Jan. 22, 1971 Netherlands 7100855[52] US. Cl 310/165, 310/114, 310/156 [51] Int. Cl. H02k 19/12 [58]Field of Search 310/45, 162, 163, 310/164,165,l56,113,114

[56] References Cited UNITED STATES PATENTS 3,614,496 10/1971'Schiethart 310/162 3,492,520 1/1970 Yates 310/156 III [111 3,743,873July 3,1973

3,495,113 2/1970 Haydon 310/156 2,927,229 3/1960 Merrill 310/2112,863,077 12/1958 Morrill 310/156 Primary ExaminerR. Skudy Att0rneyJohnP. Snyder et al.

[57] ABSTRACT A synchronous electric machine having a stator is providedwith a polyphase winding producing a rotating magnetic filed and anannular D.C. winding to produce a coaxial steady field. Sets of rotorpoles are disposed in axially spaced transverse planes and permanentmagnets consisting of ceramic material of high coercivity and havingradially inner and outer faces of opposite polarity are disposed in eachtransverse plane between the poles, the polarity of the radially outerfaces of the permanent magnets being opposed to that induced in adjacentpoles by the DC winding.

7 Claims, 7 Drawing Figures Patented July 3, 1973 3,143,313

2 Sheets-Sheet l FIGJ Patented July 3, 1973 2 Sheets-Sheet IIn!:umu:mnlniiiiiliiifiiliili SYNCHRONOUS ELECTRIC MACHINE Thisinvention relates to a synchronous electric machine comprising a statorprovided with a polyphase winding and an annular winding to produce aco-axial steady field and a rotor, the poles of which are disposed inaxially spaced transverse planes. A machine of this kind is disclosed inUS. Pat. No. 3,614,496.

The object of the invention is to improve the known machine byincreasing the useful flux. To this end, according to the invention,permanent magnets having the same polarity in the radial direction aredisposed in each transverse plane between the poles, the polarity beingopposed to that of the poles. The result is a machine having a favorableratio between the useful flex and the emerging flux, the latter termbeing used to denote the flux extending through the housing and therotor shaft.

The permanent magnets may be constructed either in the form of segmentsof a circle or be plate-shaped. A plate-shaped magnet can be covered bya soft-iron pole shoe, the flux being increased by making the axiallength of the plate greater than the length of the stack of rotorlaminations. In the case of a plate-shaped magnet, the distance to theedge of the stack of rotor laminations is greater than in the case of amagnet in the form of a segment of a circle adapted to the rotor shape.To limit the leakage flux, when plate-shaped magnets are used, it ispreferable to form the stack of rotor laminations with an opening oneither side of each magnet.

The invention will be explained in detail with reference to exemplifiedembodiments.

FIG. 1 is a longitudinal section through a machine according to theinvention;

FIG. 2a diagrammatically illustrates the value of the various fluxcomponents in the case of a machine without permanent magnets while;

FIG. 2b shows the value of the various flux components in the case of amachine with permanent magnets.

FIG. 3a is a cross-section on the line III-III in FIG. 1 and;

FIG. 3b is a longitudinal section and partial elevation of the rotorshown in FIG. 3a;

FIG. 4a is a cross-section through a rotor having plate-shaped magnetsand FIG. 4b is alongitudinal section and partial elevation of the rotorshown in FIG. 4a.

The stationary part or the stator of the motor comprises asub-stantially cylindrical housing 1, with plates 2 and 3 at either end.The plates 2, 3 are connected to the housing 1 by bolts 4, 5 and havebores for the passage of the rotor shaft 6. The shaft 6 is mounted inthe plates 2 and 3 by ballbearings 7, 8 respectively which are closed byrings 9, 10 respectively. The felt ring 11 is disposed between the ring9 and the plate 2 and a felt ring 12 is disposed between the ring 10 andthe plate 3. The left-hand part of the shaft in the drawing has a bladedwheel 13 which acts as a fan and which is shielded by a plate 14 securedby bolts 15 to the housing 1. A keyway 16 is formed in the right-handpart of the shaft. The DC. winding 17 energizes the motor. Laminatedstator cores l8 and 19 are disposed on either side of a spacer ringsurrounding the winding 17 and have a single-phase or poly-phase winding20. The winding 20 is constructed from coils or groups of coils whosecircumferential dimensions are substantially equivalent to the polepitch of different polarity as disclosed in copending application Ser.No. 131,596, filed Apr. 6, 1971 and assigned in common herewith. Analternating or rotating field is produced by means of the winding 20.

The two end portions of the shaft 6 consist of non-magnetizablematerial, while the larger-diameter middle part 6 consists ofmagnetizable material. Laminated poles provided with cages are disposedon the middle part in two axially spaced planes. The left-hand cage inthe drawing, comprising bars 27, is axially bounded by rings 30 and 32respectively, while the bars 27' of the right-hand cage end in the rings34 and 36 respectively. A stack of laminations which forms a pole isdisposed between each pair of rings. Each stack of laminations comprisesan annular main member and one or more radially projecting parts whichform the actual poles 23, 24, and 25, 26 respectively.

.The outside of the main pole member is grooved to receive the innermostparts of the bars 27 and 27'. The axial width of the poles correspondsto that of the associated stator cores 18 and 19. A spacer ring 22 ofmagnetizable material is disposed on the central part 6' between the twopoles and determines the required spacing between the poles.

The concentric excitation winding 17 carries direct current duringoperation and produces an axially directed steady field in the housingand in the shaft, said field being closed by the stator cores and thepoles. The polarity of the poles is determined by the direction of saidfield. In addition to the low power consumption, namely under no-loadconditions, as already mentioned, an important advantage of the motor isthat a controllable field can be produced without co-rotating windingsand slip rings and brushes. According to the invention, permanentmagnets 37, 38 (FIG. 3a) are disposed between the poles on the rotor.The spacing between the permanent magnets 37, 38 as far as the bottom ofthe rotor slot should be kept small in order to limit the leakage flux.The axial length of the magnets 37, 38 is substantially equal to that ofthe rotor laminations.

FIG. 2a diagrammatically illustrates the value of the emerging flux andthe useful flux together with the total flux for one half of the machinewithout the provision of permanent magnets. It has been assumed that theflux in the space between the poles is 10 percent of the flux beneaththe poles. By the provision of the permanent magnets, the flux in thebetween-pole space becomes 55 percent with the opposite sign, it beingassumed that about 50 percent of the excitation flux can be obtainedwith ceramic material. By the provision of the permanent magnets, theuseful flux increases from 45 to percent, i.e., a 67 percent increase,while the emerging flux drops from 45 to 25 percent, i.e., a drop of 55percent. The values obtained are given in FIG. 2b. In the embodimentshown in FIG. 4a, the permanent magnets are constructed as plates 39, 40covered by soft iron pole shoes 41, 42. In order to reduce the fluxleakage, openings 43, 44 and 45, 46 are formed on either side of themagnets. The axial length of the magnets 39, 40 is greater than that ofthe set of rotor laminations.

The advantages of the provision of permanent magnets in the case ofgenerator operation are an improvement to dynamic behavior, for examplein the case of What I claim is: 1. A synchronous AC. motor comprising,in combination:

a housing having a pair of axially spaced core members disposed therein;

D.C. winding means disposed between said core members for establishing aclosed D.C. magnetic field extending axially within said housing andpassing radially through said core members;

A.C. winding means extending through said core members andcircumferentially of said housing for establishing a rotating magneticfield within said housing;

a rotor journalled in said housing concentrically of said core membersand said winding means, said rotor including a shaft having opposite endportions formed of non-magnetizable material and an intermediate portionjoining said opposite end portions which is of magnetizable material,said intermediate portion of the shaft being surrounded by said coremembers and being of an axial length to extend therebeyond, said rotoralso including a pair of squirrel cage winding means fixed to saidintermediate portion of the shaft, each said squirrel cage winding meansincluding circumferentially spaced electrically conducting bars andaxially spaced end rings between which said bars extend and which endrings are disposed in planes substantially straddling a respective coremember and a pole piece disposed between said end rings, each pole piecepresenting a plurality of radially projecting poles through which someof said conducting bars extend and said poles being separated bycircumferentially equidistant radially recessed portions whereby saidD.C. winding means induces said D.C. magnetic field to pass axiallythrough said intermediate portion of the shaft and radially through saidsaid poles to said core members; and

a plurality of permanent magnets disposed within each squirrel cagewinding, one of said permanent magnets being disposed in each of saidradially recessed portions of said pole pieces and presenting radiallyinner and outer surfaces of opposite polarity in which the radiallyouter surface of each permanent magnet is of polarity opposite to thatinduced by said D.C. winding means in the poles of that squirrel cagewinding with which such perma- 55 nent magnet is associated.

2. A synchronous electric machine according to claim 1, characterized inthat the permanent magnets are in the form of segments of a circle.

3. A synchronous electric machine according to claim 1, characterized inthat the permanent magnets are plate-shaped and are each bounded by asoft-iron pole shoe having the shape of a segment of a circle.

4. A synchronous electric machine according to claim 1, characterized inthat the axial length of the permanent magnet is greater than that ofthe squirrel cage winding means.

5. A synchronous electric machine according to claim 1, characterized inthat the permanent magnets consist of ceramic material of highcoercivity.

6. A synchronous electric machine according to claim 3 characterized inthat axially extending openings are formed in each pole piece adjacentthe end regions of said radially recessed portions.

7. A synchronous electric motor comprising, in combination:

a housing having a pair of axially spaced annular core members therein;

annular D.C. winding means disposed between said core members forestablishing a closed D.C. magnetic field extending axially within saidhousing and passing radially through said core members;

A.C. winding means extending through said core members andcircumferentially of said housing for establishing a rotating magneticfield within said housing;

a rotor journalled in said housing concentrically of said core membersand of said winding means, said rotor including a pair of axially spacedsquirrel cage winding means disposed in registry respectively with saidcore members and each including an annular pole piece havingcircumferentially spaced radially projecting poles defining recessedregions therebetween, the poles of one squirrel cage winding means beingdisposed in axial alignment with the recessed regions of the othersquirrel cage winding means, said rotor also including a shaftintermediate portion of magnetizable material projecting through bothsaid squirrel cage winding means and upon which said annular pole piecesare engaged; and

a permanent magnet associated with each of said recessed regions, eachpermanent magnet having radially spaced inner and outer surfaces ofopposite polarity in which'the inner surface is disposed in closeproximity to said shaft intermediate portion and the outer surface is ofpolarity opposite to that induced in the associated pole piece by saidD.C.

magnetic field.

1. A synchronous A.C. motor comprising, in combination: a housing havinga pair of axially spaced core members disposed therein; D.C. windingmeans disposed between said core members for establishing a closed D.C.magnetic field extending axially within said housing and passingradially through said core members; A.C. winding means extending throughsaid core members and circumferentially of said housing for establishinga rotating magnetic field within said housing; a rotor journalled insaid housing concentrically of said core members and said winding means,said rotor including a shaft having opposite end portions formed ofnon-magnetizable material and an intermediate portion joining saidopposite end portions which is of magnetizable material, saidintermediate portion of the shaft being surrounded by said core membersand being of an axial length to extend therebeyond, said rotor alsoincluding a pair of squirrel cage winding means fixed to saidintermediate portion of the shaft, each said squirrel cage winding meansincluding circumferentially spaced electrically conducting bars andaxially spaced end rings between which said bars extend and which endrings are disposed in planes substantially straddling a respective coremember and a pole piece disposed between said end rings, each pole piecepresenting a plurality of radially projecting poles through which someof said conducting bars extend and said poles being separated bycircumferentially equidistant radially recessed portions whereby saidD.C. winding means induces said D.C. magnetic field to pass axiallythrough said intermediate portion of the shaft and radially through saidsaid poles to said core members; and a plurality of permanent magnetsdisposed within each squirrel cage winding, one of said permanentmagnets being disposed in each of said radially recessed portions ofsaid pole pieces and presenting radially inner and outer surfaces ofopposite polarity in which the radially outer surface of each permanentmagnet is of polarity opposite to that induced by said D.C. windingmeans in the poles of that squirrel cage winding with which suchpermanent magnet is associated.
 2. A synchronous electric machineaccording to claim 1, characterized in that the permanent magnets are inthe form of segments of a circle.
 3. A synchronous electric machineaccording to claim 1, characterized in that the permanent magnets areplate-shaped and are each bounded by a soft-iron pole shoe having theshape of a segment of a circle.
 4. A synchronous electric machineaccording to claim 1, characterized in that the axial length of thepermanent magnet is greater than that of the squirrel cage windingmeans.
 5. A synchronous electric machine according to claim 1,characterized in that the permanent magnets consist of ceramic materialof high coercivity.
 6. A synchronous electric machine according to claim3 characterized in that axially extending openings are formed in eachpole piece adjacent the end regions of said radially recessed portions.7. A synchronous electric motor comprising, in combination: a housinghaving a pair of axially spaced annular core members therein; annularD.C. winding means disposed between said core members for establishing aclosed D.C. magnetic field extending axially within said housing andpassing radially through said core members; A.C. winding means extendingthrough said core members and circumferentially of said housing forestablishing a rotating magnetic field within said housing; a rotorjournalled in said housing cOncentrically of said core members and ofsaid winding means, said rotor including a pair of axially spacedsquirrel cage winding means disposed in registry respectively with saidcore members and each including an annular pole piece havingcircumferentially spaced radially projecting poles defining recessedregions therebetween, the poles of one squirrel cage winding means beingdisposed in axial alignment with the recessed regions of the othersquirrel cage winding means, said rotor also including a shaftintermediate portion of magnetizable material projecting through bothsaid squirrel cage winding means and upon which said annular pole piecesare engaged; and a permanent magnet associated with each of saidrecessed regions, each permanent magnet having radially spaced inner andouter surfaces of opposite polarity in which the inner surface isdisposed in close proximity to said shaft intermediate portion and theouter surface is of polarity opposite to that induced in the associatedpole piece by said D.C. magnetic field.